URL Rewrite / Embedded / Custom 404

this is my gallery http://jmbphotographic.co.uk/gallery.php

this is my custom 404 http://jmbphotographic.co.uk/404.html

and this is what ACTUALLY shows up with ANY incorrect file or directory http://jmbphotographic.co.uk/galle.php

The URL Rewrite for the 404 makes everything stop working, is there anyway that i can have my custom 404 show up instead of what is currently appearing?